1. Field of the Invention
The present invention relates to a coordinate measuring apparatus measuring a shape of a measured object by emitting light at the measured object and capturing an image thereof.
2. Description of Related Art
Conventionally, a shape measuring apparatus is known in which a surface shape of a measured object (hereafter referred to as a “work piece” or “workpiece”) is measured by scanning a surface of the work piece with a probe and acquiring position coordinates, for example, of each portion of the work piece. Known examples of such a shape measuring apparatus include a shape measuring apparatus measuring position coordinates of a work piece and including a measurer (stylus) making contact with a surface of the work piece, and a non-contact-type shape measuring apparatus in which measurement is performed by an optical system, without a measurer (stylus) touching a surface of a work piece.
A non-contact-type surface shape measuring apparatus of this kind includes a emitting optical system and a non-contact-type probe, the emitting optical system emitting light along a predetermined plane at a work piece from a predetermined emitting direction, and the non-contact-type probe being configured by an image capture apparatus capturing an image of a shape of light that is incident on the surface of the work piece. The emitting optical system includes a light source emitting laser light having a straight-line shape (a point laser) toward the work piece, and an emitted light adjuster adjusting the laser light emitted by the light source into a planar shape (sheet-like shape). According to this emitting optical system, emitted light (also referred to as a line laser, a laser sheet, a laser light sheet, etc.) is emitted along the predetermined plane toward the work piece surface, and light is incident at positions where the emitted light and the work piece surface intersect, the incident light corresponding to a shape thereof (i.e., light having a shape in an contour of the work piece). The image capture apparatus captures an image of the work piece (the incident light incident on the surface) from a predetermined image capture direction, which is different from the emitting direction of the light source.
With the above-noted configuration, the light incident on the work piece surface (i.e., spatial coordinates of an contour shape of the work piece) can be calculated using a triangulation method, based on the emitting direction of the emitting optical system, the image capture direction of the image capture apparatus, a distance between the emitting optical system and the image capture apparatus, and the captured image.
In the non-contact-type surface shape measuring apparatus of this kind, the emitting direction of the emitting optical system and the image capture direction are different, as noted above. Accordingly, in a case where a distance between the probe and the work piece becomes too small or too large, for example, the light incident on the work piece surface does not strike within an image capture region of the image capture apparatus and image capture is impossible. Verification as to whether the distance between the probe and the work piece is appropriate can be performed on a display; however, in such a case, an operator must visually register both the display and a sample stage, thus leading to reduced operability.
Conventionally, in order to resolve this issue, an instruction light emitter emitting instruction light having a wavelength different from that of the laser has been provided in addition to the probe, and in a case where the laser is outside the range where measurement is possible, the instruction light emitter is turned on and the instruction light is emitted at the work piece, thereby enabling verification as to whether the laser light is positioned within the range where measurement of the work piece is possible (Japanese Patent Laid-open Publication No. 2012-127805).
However, in the method described in Japanese Patent Laid-open Publication No. 2012-127805, in order to verify whether the laser light is positioned within an image capture region of the work piece, the instruction light emitter having a wavelength different from that of the laser light must be separately provided, which may increase manufacturing costs of the apparatus. In addition, the instruction light emitter is turned on separately from the laser light, therefore increasing power consumption, which may lead to heat drift or malfunction due to heat generated by an illumination light emitter. Even when a cooling fan is attached, vibration caused by the cooling fan may be transmitted to the probe, and thus measurement accuracy may be reduced. Moreover, in such a case, air holes must be provided in order to cool the measurement probe, and this has also been linked to a reduction in environmental resistance.